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    <section class="main-section" id="Introduction">
      <header >Introduction</header>
      <p>JavaScript is a cross-platform, object-oriented scripting language. It is a small and lightweight language.
        Inside a host environment (for example, a web browser), JavaScript can be connected to the objects of its
        environment to provide programmatic control over them.

      <p>JavaScript contains a standard library of objects, such as Array, Date, and Math, and a core set of language
        elements such as operators, control structures, and statements. Core JavaScript can be extended for a variety of
        purposes by supplementing it with additional objects; for example:
      </p>
      <ul>
        <li>

          Client-side JavaScript extends the core language by supplying objects to control a browser and its Document
          Object Model (DOM). For example, client-side extensions allow an application to place elements on an HTML form
          and respond to user events such as mouse clicks, form input, and page navigation.
        </li>
        <li>

          Server-side JavaScript extends the core language by supplying objects relevant to running JavaScript on a
          server. For example, server-side extensions allow an application to communicate with a database, provide
          continuity of information from one invocation to another of the application, or perform file manipulations on
          a server.</p>
        </li>
        <li>

          Client-side JavaScript extends the core language by supplying objects to control a browser and its Document
          Object Model (DOM). For example, client-side extensions allow an application to place elements on an HTML form
          and respond to user events such as mouse clicks, form input, and page navigation.
        </li>
        <li>

          Server-side JavaScript extends the core language by supplying objects relevant to running JavaScript on a
          server. For example, server-side extensions allow an application to communicate with a database, provide
          continuity of information from one invocation to another of the application, or perform file manipulations on
          a server.</p>
        </li>
        <li>

          Client-side JavaScript extends the core language by supplying objects to control a browser and its Document
          Object Model (DOM). For example, client-side extensions allow an application to place elements on an HTML form
          and respond to user events such as mouse clicks, form input, and page navigation.
        </li>
        <li>

          Server-side JavaScript extends the core language by supplying objects relevant to running JavaScript on a
          server. For example, server-side extensions allow an application to communicate with a database, provide
          continuity of information from one invocation to another of the application, or perform file manipulations on
          a server.</p>
        </li>
        <li>

          Client-side JavaScript extends the core language by supplying objects to control a browser and its Document
          Object Model (DOM). For example, client-side extensions allow an application to place elements on an HTML form
          and respond to user events such as mouse clicks, form input, and page navigation.
        </li>
        <li>

          Server-side JavaScript extends the core language by supplying objects relevant to running JavaScript on a
          server. For example, server-side extensions allow an application to communicate with a database, provide
          continuity of information from one invocation to another of the application, or perform file manipulations on
          a server.</p>
        </li>
      </ul>
      <p>p num :2</p>
    </section>
    <section class="main-section" id="What_you_should_already_know">
      <header>What you should already know</header>
      <p>This guide assumes you have the following basic background:
        A general understanding of the Internet and the World Wide Web (WWW).
        Good working knowledge of HyperText Markup Language (HTML).
        Some programming experience. If you are new to programming, try one of the tutorials linked on the main page
        about JavaScript.</p>
      <p>p num :2</p>
    </section>
    <section class="main-section" id="JavaScript_and_Java">
      <header>JavaScript and Java</header>
      <p>
        JavaScript and Java are similar in some ways but fundamentally different in some others. The JavaScript language
        resembles Java but does not have Java's static typing and strong type checking. JavaScript follows most Java
        expression syntax, naming conventions and basic control-flow constructs which was the reason why it was renamed
        from LiveScript to JavaScript.
      </p>
      <p>
        In contrast to Java's compile-time system of classes built by declarations, JavaScript supports a runtime system
        based on a small number of data types representing numeric, Boolean, and string values. JavaScript has a
        prototype-based object model instead of the more common class-based object model. The prototype-based model
        provides dynamic inheritance; that is, what is inherited can vary for individual objects. JavaScript also
        supports functions without any special declarative requirements. Functions can be properties of objects,
        executing as loosely typed methods.
      </p>
      <p>
        JavaScript is a very free-form language compared to Java. You do not have to declare all variables, classes, and
        methods. You do not have to be concerned with whether methods are public, private, or protected, and you do not
        have to implement interfaces. Variables, parameters, and function return types are not explicitly typed.
      </p>
    </section>
    <section class="main-section" id="Hello_world">
      <header>Hello world</header>
      <p>To get started with writing JavaScript, open the Scratchpad and write your first "Hello world" JavaScript code:
      </p>
      <p><code>function greetMe(yourName) { alert("Hello " + yourName); }
greetMe("World");</code></p>
      <p>看有没有该项目，然后在电脑里搜索“WINFILE”和“XVVST.EXE”文件把它们删除（在XVVST。
      </p>
    </section>
    <section class="main-section" id="Variables">
      <header>Variables</header>
      <code>function greetMe(yourName) { alert("Hello " + yourName); }
greetMe("World");</code><code>function greetMe(yourName) { alert("Hello " + yourName); }
greetMe("World");</code><code>function greetMe(yourName) { alert("Hello " + yourName); }
greetMe("World");</code><code>function greetMe(yourName) { alert("Hello " + yourName); }
greetMe("World");</code><code>function greetMe(yourName) { alert("Hello " + yourName); }
greetMe("World");</code>
      <p>You use variables as symbolic names for values in your application. The names of variables, called identifiers,
        conform to certain rules.
      </p>
      <p>
        A JavaScript identifier must start with a letter, underscore (_), or dollar sign ($); subsequent characters can
        also be digits (0-9). Because JavaScript is case sensitive, letters include the characters "A" through "Z"
        (uppercase) and the characters "a" through "z" (lowercase).
      </p>
      <p>
        You can use ISO 8859-1 or Unicode letters such as å and ü in identifiers. You can also use the Unicode escape
        sequences as characters in identifiers. Some examples of legal names are Number_hits, temp99, and _name.
      </p>

    </section>
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    <header>JavaScript </header>
    <ul>
      <li><a href="#Introduction" class="nav-link">Introduction</a></li>
      <li><a href="#What_you_should_already_know" class="nav-link">What you should already know</a></li>
      <li><a href="#JavaScript_and_Java" class="nav-link">JavaScript and Java</a></li>
      <li><a href="#Hello_world" class="nav-link">Hello world</a></li>
      <li><a href="#Variables" class="nav-link">Variables</a></li>
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